Enhanced intra prediction mode signaling

An apparatus for decoding a bitstream for a video signal, the apparatus comprising:

• an intra predicting unit configured to:
• obtain residual samples for a current block
• determine a candidate mode list based on intra prediction modes of neighboring blocks adjacent to the current block, the candidate mode list comprising at least three candidate prediction modes,
• obtain flag information from the bitstream, the flag information indicating whether an intra prediction mode of the current block is derived from a neighboring block,
• based on the flag information indicating that the intra prediction mode of the current block is not derived from a neighboring block:
• obtain intra prediction mode information of the current block from the bitstream,
• reorder the at least three candidate prediction modes such that a lower index is assigned to a candidate prediction mode having a lower value,
• obtain the intra prediction mode of the current block based on the intra prediction mode information and the at least three reordered candidate prediction modes,
• obtain predicted samples for the current block by performing an intra prediction for the current block based on the obtained intra prediction mode, and
• decode the current block based on the predicted samples and the residual samples.

A method of encoding a video signal, the method performed by an encoding apparatus and comprising:

• obtaining an intra prediction mode of a current block;
• obtaining predicted samples for the current block by performing an intra prediction for the current block based on the obtained intra prediction mode;
• obtaining residual samples for the current block based on the predicted samples;
• encoding the residual samples;
• determining a candidate mode list based on intra prediction modes of neighboring blocks adjacent to the current block, the candidate mode list comprising at least three candidate prediction modes;
• encoding flag information into a bitstream, the flag information indicating whether the intra prediction mode of the current block is derived from a neighboring block;
• based on the flag information indicating that the intra prediction mode of the current block is not derived from a neighboring block:
• reordering the at least three candidate prediction modes such that a lower index is assigned to a candidate prediction mode having a lower value;
• and
• encoding intra prediction mode information of the current block into the bitstream based on the intra prediction mode of the current block and the at least three reordered candidate prediction modes.

A non-transitory computer-readable storage medium storing a bitstream generated by an encoding method, the encoding method comprising:

• obtaining an intra prediction mode of a current block;
• obtaining predicted samples for the current block by performing an intra prediction for the current block based on the obtained intra prediction mode;
• obtaining residual samples for the current block based on the predicted samples;
• encoding the residual samples;
• determining a candidate mode list based on intra prediction modes of neighboring blocks adjacent to the current block, the candidate mode list comprising at least three candidate prediction modes;
• encoding flag information into a bitstream, the flag information indicating whether the intra prediction mode of the current block is derived from a neighboring block;
• based on the flag information indicating that the intra prediction mode of the current block is not derived from a neighboring block:
• reordering the at least three candidate prediction modes such that a lower index is assigned to a candidate prediction mode having a lower value;
• and
• encoding intra prediction mode information of the current block into the bitstream based on the intra prediction mode of the current block and the at least three reordered candidate prediction modes.